1. Technical Field
This disclosure relates to ambient noise compensation, and more particularly to an ambient noise compensation system that prevents uncontrolled gain adjustments.
2. Related Art
Some ambient noise estimation involves a form of noise smoothing that may track slowly varying signals. If an echo canceller is not successful in removing an echo entirely, this may affect ambient noise estimation. Echo artifacts may be of short duration.
In some cases the excitation signal may be slowly varying. For example, when a call is made and received between two vehicles. One vehicle may be traveling on a concrete highway, perhaps it is a convertible. High levels of constant noise may mask or exist on portions of the excitation signal received and then played in the second car. This downlink noise may be known as an excitation noise. An echo canceller may reduce a portion of this noise, but if the true ambient noise in the enclosure is very low, then the residual noise may remain after an echo canceller processes. The signal may also dominate a microphone signal. Under these circumstances, the ambient noise may be overestimated. When this occurs, a feedback loop may be created where an increase in the gain of the excitation signal (or excitation noise) may cause an increase in the estimated ambient noise. This condition may cause a gain increase in the excitation signal (or excitation noise).